A format is a function [realm] => formatter, which should return nil for unsupported realms.

This namespace contains utilities to create and use such functions.

A formatter is a function [resolve] => translator, which create a translator,
potentially based on other translators for a realm returned by the resolve function.

This namespace contains a collection of some standard formatters and utilities to build others.

Translators represent the core functionality of translating between
internal and external representations of values.

Note that in general, translators should validate the external
values, throwing [[format-error]] for invalid values, but should assume
that internal values are valid, using [[active.data.realm.attach]] so add optional validation.